Selecting which main base station for an infill base station to monitor in a mobile radio system

Abstract

A method for selecting a channel and a base station in a mobile radio system, the geographical coverage area of which is divided into radio cells, each radio cell including a main base station indicated by an identifier, and at least one of the radio cells including at least one infill base station. In the method, the main base station signals with subscriber stations on a control channel having a downlink frequency for signalling from a base station to a subscriber station and an uplink frequency for signalling from a subscriber station to a base station. Each infill base station monitors the subscriber stations at the uplink frequency of the control channel of the respective main base station. To select the best possible main base station, each infill base station measures the quality of the control channels of predetermined ones of the main base stations and selects, on the basis of the quality of the downlink frequencies of the control channels, a main base station the uplink frequency of the control channel of which it begins to monitor.

I claim: 
     
       1. A method for selecting a channel in a mobile radio system, the geographical coverage area of which is divided into a plurality of radio cells, each radio cell comprising a main base station indicated by an identifier, at least one said radio cell further comprising at least one infill base station, said method comprising the steps of: (a) signalling by each said main base station with subscriber stations on a respective control channel having a respective downlink frequency for signalling from the respective base stations to subscriber stations and a respective uplink frequency for signalling from each respective subscriber station to a respective said base stations,   (b) monitoring by a said infill base station respective of the subscriber stations at the uplink frequency of the control channel of a respective said main base station,   (c) measuring by the respective infill base station the quality of the downlink control channels of predetermined ones of said main base stations, and   (d) selecting by the respective infill base station on the basis of the quality of the downlink frequencies of said downlink control channels, a one of said main base stations the uplink frequency of the control channel of which main base station the respective infill base station begins to monitor in continuation of or in place of the one being monitored in step (b).   
     
     
       2. The method for selecting a channel according to claim 1, wherein: step (c) further includes searching by said infill base station in a data base thereof for the identifiers of said predetermined main base stations and for the control channels used by said predetermined main base stations,   step (c) further includes tuning by said infill base station of itself to monitor the downlink frequencies of the control channels of said predetermined main base stations in turn,   step (c) further includes measuring by said infill base station of the quality of each message received at the respective downlink frequency of the respective said control channels,   step (d) further includes selecting by said infill base station for monitoring the respective said main base station which has the best message quality,   step (d) further includes informing by said infill base station an exchange of said mobile radio system that said infill base station is beginning to monitor the uplink frequency of said control channel of the selected said main base station, and   step (d) further includes beginning by said infill base station to monitor the uplink frequency of the respective said control channel of said selected main base station.   
     
     
       3. The method for selecting a channel according to claim 2, wherein: step (c) further includes discovering by said infill base station, when being tuned to monitor the downlink frequencies of the control channels of respective of said main base stations, at said frequencies, an identifier sent by a main base station,   step (c) further includes comparing by said infill base station of said discovered identifier with the identifiers of said predetermined main base stations in said data base thereof, and   step (c) further includes said infill base station performing as a result of the comparison, if said identifier is of one of said predetermined main base stations, measurements of message quality, and   step (d) further includes informing by said infill base station said exchange of said mobile radio system of the identifier of said selected main base station.   
     
     
       4. The method for selecting a channel according to claim 2, further comprising: said infill base station receiving from a subscriber station a request for establishing a connection,   said infill base station transmitting information as to said request for establishing a connection, received from said subscriber station, to said exchange of said mobile radio system,   said exchange selecting from a data base of said exchange a free traffic channel for the traffic between said subscriber station from which said request was received and said infill base station,   said infill base station receiving from said exchange a command to move onto said traffic channel in the traffic with said subscriber station, and   said infill base station moving onto said traffic channel.   
     
     
       5. The method for selecting a channel according to claim 3, further comprising: said infill base station receiving from a subscriber station a request for establishing a connection,   said infill base station transmitting information as to said request for establishing a connection, received from said subscriber station, to said exchange of said mobile radio system,   said exchange selecting from a data base of said exchange a free traffic channel for the traffic between said subscriber station from which said request was received and said infill base station,   said infill base station receiving from said exchange a command to move onto said traffic channel in the traffic with said subscriber station, and   said infill base station moving onto said traffic channel.   
     
     
       6. The channel management method according to claim 2, wherein: in practicing step (c), in case the quality of a message received at the downlink frequency of a respective said control channel is not sufficient, said infill base station tuning to monitor the control channel of the main base station of some other said radio cell and thereby searching for a best possible control channel for selection in step (d).   
     
     
       7. The channel management method according to claim 3, wherein: in practicing step (c), in case the quality of a message received at the downlink frequency of a respective said control channel is not sufficient, said infill base station tuning to monitor the control channel of the main base station of some other said radio cell and thereby searching for a best possible control channel for selection in step (d).   
     
     
       8. The channel management method according to claim 4, wherein: in practicing step (c), in case the quality of a message received at the downlink frequency of a respective said control channel is not sufficient, said infill base station tuning to monitor the control channel of the main base station of some other said radio cell and thereby searching for a best possible control channel for selection in step (d).   
     
     
       9. The channel management method according to claim 5, wherein: in practicing step (c) in case the quality of a message received at the downlink frequency of a respective said control channel is not sufficient, said infill base station tuning to monitor the control channel of the main base station of some other said radio cell and thereby searching for a best possible control channel for selection in step (d).   
     
     
       10. An infill base station of a mobile radio system, comprising: a radio transceiver,   a controller unit for controlling said infill base station, comprising means for measuring the quality of the control channels of a plurality of predetermined main base stations of said mobile radio system and for selecting, on the basis of the quality of the downlink frequencies of the control channels, the main base station the uplink frequency of the control channel of which the base station begins to monitor.   
     
     
       11. The infill base station according to claim 10, further comprising: a data base storing identifiers of said predetermined main base stations with which said infill base station is allowed to establish a connection of monitoring.